Reproduce surface-gas volume from one completed cylinder pressure window and compare a separate same-unit record without estimating SAC, duration, reserve or dive safety.
Specialist tool for Scuba Diving1 documented formula2 real workflowsPrivate in your browser
Use this result well
A quick decision brief for this specific tool
Inputs that matter
One de-identified completed-record scope and basis; explicit imperial psi/scf or metric bar/L system; named exact cylinder-rating, completed pressure-window and independent gas-use records; start/end gauge pressure; matching rated free-gas capacity/rated pressure; and a same-unit independent surface-gas volume used
Output to expect
Preserved record provenance, completed pressure change, cylinder constant, reproduced surface-gas volume used, independent same-unit volume and signed reproduced-minus-independent gas-use difference
How it works
Subtract the completed gauge readings, divide the matching rated free-gas capacity by its rated pressure, multiply that cylinder constant by the pressure change and subtract the independent same-window gas-use record; do not introduce time, ATA, SAC/RMV, at-depth demand or duration
Confirm the rating pair belongs to the exact cylinder record and distinguishes rated free-gas capacity from water capacity, working/test/service pressure and another model's data; review actual fill, temperature, compressibility, gauge accuracy, gas mix and equipment condition separately.
Use the signed difference only as a completed-record review flag. Follow current training, operator procedures, the responsible dive plan and qualified supervision for reserves, turn pressure, ascent/decompression, buddy/team gas, future duration, equipment acceptance and every safety decision.
Choose your path
Built around the job you need to finish
Reproduce the surface-gas volume represented by one completed cylinder pressure window and compare a separately prepared same-unit record without calculating SAC/RMV, duration, reserves or a dive verdict.
Certified diver reconciling one completed pressure record
Check a copied start/end gauge window against a separate gas-use total without receiving another rate or future-duration estimate.
Name the completed record and exact cylinder rating pair, select one coherent unit system, copy both gauge readings and compare the reproduced volume with the independent record.
Can identify the direction and size of a record mismatch while reserve, ascent, equipment and safety decisions remain outside the worksheet.
Instructor reviewing a supervised cylinder exercise
Teach why rated free-gas capacity, rated pressure and water capacity are different records and why a cylinder nickname is insufficient.
Load the 80-scf-at-3000-psi exercise, inspect the pressure change and cylinder constant, then alter the independent volume and explain the signed difference.
The learner can reproduce completed gas volume without inferring SAC, workload, at-depth demand or safe remaining time.
Equipment-record auditor comparing metric logs
Preserve the exact product/rating provenance and compare an archived metric pressure window with a separately prepared liter total.
Select bar/L, retain model-specific rating and pressure-window records, copy the metric checkpoints, save one deliberate reviewed run and export the provenance.
Receives an auditable same-unit comparison while actual fill, temperature, compressibility, gauge and equipment acceptance remain external.
Authoritative checks for this tool
Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.
Copy the rated free-gas capacity and the rated pressure that belong together in the exact model or rating record. Internal water volume, test pressure, service markings, another cylinder's rating and an assumed actual fill are not interchangeable inputs.
Both readings must come from the same named completed pressure-window record and use the selected pressure unit. This subtraction does not establish when, where or why the pressure changed.
The signed difference preserves mismatch direction. Zero means only that the two copied totals agree under this linear rating approximation; it does not validate the cylinder, gauge, fill, equipment, record or dive.
Reproduced gas used = Pressure change × Cylinder constant; Difference = Reproduced − Independent
Updated: August 2026
Example Scenarios
An instructor records a completed 3000-to-1800 psi window for a source labelled 80 scf at 3000 psi and an independent 32 scf total. The worksheet reproduces 32 scf and a zero difference without calculating a breathing rate or allowable time.
A de-identified record uses 2400 L at 200 bar with a completed 200-to-125 bar window. The worksheet reproduces 900 L; an independent 890 L record produces a +10 L review flag.
A reviewer finds that an independently copied total is larger than the volume reproduced from the same rating and pressure window. The negative signed difference is routed back to the record and equipment owners rather than converted into a safety conclusion.
FAQ
No. SAC and RMV require a defined time interval and, for normalized retrospective rates, an appropriate ambient-pressure record. This worksheet deliberately stops at the total surface-gas volume represented by one completed pressure window.
Use the rated free-gas or air capacity paired with its exact rated pressure in the reviewed product or rating record. Do not substitute internal water capacity, test pressure, a cylinder nickname or a value from another model.
The pressure readings and rated pressure must both use psi or both use bar, while the capacity and independent volume must both use scf or both use liters. The page labels the result from that selection but cannot detect a mislabeled source record.
Only that the independently entered volume equals the volume reproduced by this arithmetic for the copied inputs. It does not prove the gauge, cylinder rating, fill, temperature/compressibility assumptions, equipment condition or source record is correct.
No. It contains no time, ambient pressure, team demand, ascent/decompression, contingency or operational authorization. Apply current training, operator procedures, the responsible dive plan and qualified supervision outside this record check.
About Completed Cylinder Gas-Use Record
Use this retrospective worksheet for one already completed, source-labelled cylinder pressure window. Copy the exact rated free-gas capacity and matching rated pressure for that cylinder record, reproduce the surface-gas volume represented by the gauge-pressure change, and compare a separately prepared same-unit total. It does not use time or depth and does not create a gas plan.
